A mistake never comes alone. That is one of the universal chess truths.
17. f2f3 Another innacuracy. 17... h5g7  18. h2g3 The critical moment in the game. 18... h8h5 Ding is careless with the c2-bishop. He certainly miscalculated something. 19. e2e4 Now the bishop is trapped and will eventually be captured. Black won't have enough compensation for the piece. Although there's still a lot of play left, there is a major shift in the assessment of the position. Furthermore, Gukesh had a large advantage on the clock at this point.